Fuel efficiency and exhaust pollutant levels are viewed as increasingly important characteristics for all vehicles. This has led to a very high proportion of vehicle engines being fitted with turbochargers which often incorporate an exhaust gas recirculation system. Exhaust gas recirculation (EGR) is a process used to improve engine efficiency and reduce the presence of NOx compounds in the emitted exhaust gases by recirculating a portion of the exhaust gases through the engine. In low-pressure EGR, the EGR gases are introduced upstream of the turbocharger compressor inlet. The pressure at this location is low, even in high engine boost conditions, which allows for the low pressure recirculation of the exhaust gases.
In low-pressure EGR systems, EGR gases introduced upstream of the turbocharger compressor are mixed with engine inlet air before entering the turbocharger compressor inlet. The amount of EGR gases which can be introduced may determine the extent to which engine efficiency and exhaust gas pollutant levels are improved. However, the level of recirculation possible is often limited by condensation of water droplets in the exhaust gases. As the exhaust gases are mixed with the cooler inlet air, water vapor begins to condense from the exhaust gases. This effect may be exacerbated in cold ambient conditions. Contact between the EGR gases and the walls of the duct upstream of the turbocharger compressor also contributes to the condensation. Water droplets can be undesirable at the inlet of the compressor, especially when large water droplets are formed, which may damage the compressor blades. Thus, it is desirable for the EGR gases to be introduced close to the compressor face. However, in EGR implementations where the EGR gases are introduced close to the compressor face and at the same point at which the throttling function is performed then unstable turbulent air can reduce the compressor's operational efficiency.
According to an aspect of the present disclosure, there is provided an exhaust gas recirculation (EGR) apparatus for a turbocharged internal combustion engine, the EGR apparatus comprising: an air intake duct with a throttle valve configured to control an intake air quantity flowing through the air intake duct to a turbocharger compressor; an exhaust gas recirculation inlet connected to the air intake duct downstream of the throttle valve; and an EGR valve configured to control an exhaust gas quantity recirculated to the turbocharger compressor via the exhaust gas recirculation inlet, wherein the throttle valve and the EGR valve are combined in a single valve unit in which the valves are separated by a separating element configured to substantially prevent exhaust gas from entering the air intake duct in a vicinity of the throttle valve.
Introducing recirculated exhaust gas to the air intake duct closer to the compressor face can reduce the risk of condensate droplets propagating into the air intake duct and damaging the turbocharger compressor, while positioning the throttle valve further from the compressor face gives the throttled air distance to re-stabilize before entering the turbocharger compressor. This more stable flow is desired for optimal turbocharger compressor performance. Combining the valves in a single valve unit, in which the valves can operated simultaneously, so that the air intake duct can be closed and at the same time the exhaust gas recirculation inlet can be opened (or the air intake duct opened and the exhaust gas recirculation inlet closed), for example by means of a common actuator, can realize savings in weight, complexity and cost compared to separate throttle valve and EGR valve units having dedicated actuators for example.
The valve unit can have a main valve body defining a passage through which exhaust gas flows to the exhaust gas recirculation inlet when a movable valve element of the EGR valve is in an open position, and the separating element can be disposed between the passage of the valve body and the throttle valve. This provides a simple configuration for fluidly separating the air flow in the vicinity of the throttle valve from the recirculated exhaust gas. The main valve body can be directly attached to the air intake duct.
The movable valve element of the EGR valve can be mechanically connected to a movable valve element of the throttle valve by a valve stem which passes through a gap in the separating element. However, the throttle valve can be mechanically connected to the EGR valve by any kind of linkage, gears, or other mechanism configured to allow the valves to operate in unison.
The exhaust gas recirculation inlet can comprise a conduit which fluidly connects the passage of the valve body to the interior of the air intake duct downstream of the throttle valve. This provides a simple construction by which the exhaust gas can be introduced to the air intake duct downstream of the throttle valve. The distance between the throttle valve and the point of introduction of the exhaust gas into the air intake duct, the distance between the throttle valve and the turbocharger compressor, and/or the distance between the point of introduction of the exhaust gas into the air intake duct and the turbocharger, can be varied depending on engine application and EGR usage schedules. Furthermore, installation factors and limitations such as duct size and shape can affect the positioning. The conduit can have an opening on the air intake duct. Alternatively, the conduit may extend into the air intake duct. For example, the conduit can include an end portion that extends upwardly into the air intake duct. The end portion can be curved so as to direct exhaust gas towards the turbocharger compressor. Other configurations are also possible. For example, the end portion may comprise an initial straight portion extending into the air intake duct, followed by a bend section that curves towards the turbocharger compressor, followed by a further straight section. The outlet of the end portion can be positioned centrally with respect to the air intake duct outlet.
The separating element can comprises a plate, which can be can formed as an integral cast part of the EGR apparatus or, alternatively, as a component which is inserted between the passage and the throttle valve, for example during assembly of the EGR apparatus.
The throttle valve can comprise a throttle flap. The EGR valve can comprise a lifting valve such as a poppet valve.
According to another aspect of the disclosure, there is provided an engine system, comprising: an internal combustion engine having an intake manifold and an exhaust manifold; a turbocharger mounted on the engine, the turbocharger including a turbine fluidly connected to the exhaust manifold and a compressor fluidly connected to the intake manifold; and the aforementioned exhaust gas recirculation (EGR) apparatus.
According to another aspect of the disclosure, there is provided a motor vehicle including the aforementioned engine system.
According to another aspect of the disclosure, there is provided an exhaust gas recirculation (EGR) method for an internal combustion engine with a turbocharger, the EGR method comprising: controlling, by the throttle valve, an intake air quantity flowing through an air intake duct provided with the throttle valve to a compressor of the turbocharger; and controlling, by the EGR valve which is combined with the throttle valve as a single valve unit, an exhaust gas quantity recirculated to the compressor via an exhaust gas recirculation inlet connected to the air intake duct downstream of the throttle valve; and substantially preventing, by a barrier which separates the throttle valve from the EGR valve, exhaust gas from entering the air intake duct at the throttle valve.
Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of example embodiments of the present application.